Mac OS X 10.6.3 has just been released. It is downloadable via MacOS Software Update or from Apple’s Support page in combo format. It weighs in at a rather heavy 438,7 MB for my MacBook Pro via Software update, but takes a whopping 719.23 MB of space as the combo update. It IS recommended for all Snow Leopard users, but as always, comes with the proviso: early adopters are often bug-rooters as is found in this 10.6.3 Apple Discussion thread. Remember to backup your Mac before installing any system-dependent files or updates; you don’t want this to happen (From Apple Discussion thread):

I just updated to 10.6.3 using the System Update on my first-generation MacBook Pro. I’m now getting a kernel panic at startup, and cannot boot the system.